The present invention relates to a toroidal type continuously variable transmission used as a transmission for vehicles such as automobiles and particularly, to a method of manufacturing a disk for a toroidal type continuously variable transmission.
Heretofore, speed change gears have mainly been used as transmissions for vehicles such as automobiles. The speed change gears comprises a plurality of gears, and the engagement mode of the gears is varied to transmit torque from an input shaft to an output shaft. However, in the conventional speed change gears, torque is varied stepwise and discontinuously at the time of changing the speed. Thus, the speed change gears have drawbacks such as a loss in power transmission and vibration at the time of changing the speed.
Under the circumstances, a continuously variable transmission, in which torque is not varied stepwise or discontinuously at the time of changing the speed, has recently been put to practical use. In the continuously variable transmission, no vibration occurs at the time of changing the speed, and the loss in power transmission is less than that in the speed change gears. In addition, the continuously variable transmission is fuel-efficient when it is mounted in the vehicle. As an example of the continuously variable transmission, a belt type continuously variable transmission is mounted in some type of passenger cars.
On the other hand, as an another example of the continuously variable transmission, a toroidal type continuously variable transmission has been proposed. The toroidal type continuously variable transmission comprises an input shaft rotated by a drive source such as an engine, an input disk, an output disk and power rollers. The input disk is supported on the input shaft and rotated in interlock with the input shaft. The output disk is supported on the input shaft so as to be opposed to the input disk and rotated in interlock with the output shaft. The power roller is provided swingably between the input disk and the output disk and rotatably put into contact with both disks.
The input disk and the output disk have essentially equivalent shapes to each other. One disk 80 of the input disk and the output disk will below be described in reference to FIG. 17.
The disk 80 has the shape of a disk symmetrical with respect to an axis P1. The disk 80 comprises a protrusion 81, a skirt portion 82 and a mounting hole 83 in one body. The protrusion 81 is projected in the central portion of the disk 80 along the axis P1 as viewed from the side. The skirt portion 82 is provided outside an outer periphery of the protrusion 81 and a thickness of the disk is gradually thinner along a direction from the protrusion 81 toward its outer edge. The mounting hole 83 penetrates through the protrusion 81 along the axis Pl. The mounting hole 83 accommodates the input shaft inside the hole when the disk 80 is mounted on the input shaft.
The disk 80 is provided with a traction surface 85 over the protrusion 81 and the skirt portion 82. The traction surface 85 is formed in the sectional shape of an arc whose center coincides with the axis P1 of a shaft which supports the power roller in a freely swingable manner. The traction surface 85 is formed along all the periphery of the disk 80.
The toroidal type continuously variable transmission can transmit higher torque as compared with the belt type continuously variable transmission. For this reason, it is considered that the toroidal type continuously variable transmission is effective for continuously variable transmissions for middle and large sized vehicles.
However, the toroidal type continuously variable transmission requires transmission of larger torque. For this reason, the disk 80 and the power roller receive a very large repeated bending stress and a very large repeated shearing stress as compared with general mechanical parts on which a repeated stress acts such as a gear and a bearing. Especially, the disk 80 receives a large stress on an end surface 81a of the protrusion 81.
As a method of manufacturing a disk 80 for the toroidal type continuously variable transmission, for example, a method in which a work formed in a rod shape by a rolling process is subjected to machining or a method which has been disclosed in Jpn. Pat. Appln. Publication No. 9-126289 has been employed. The method shown in Jpn. Pat. Appln. Publication No. 9-126289 is that a work as an to-be-molded object is subjected to forging so to be fashioned into a near final shape and thereafter grinding is performed on the work as a finishing process.
When the above described disk is manufactured by machining a rod-like metal base material mass, a yield is low due to machining loss and a required time for the process is long. Hence, a problem arises that a production cost is increased.
Furthermore, a base material mass used for a disk that has been formed into a rod-like shape through processes such as melting, casting, and rolling, includes most of the disk""s impurities in an area defined by a diameter that is 30% or less of the outer diameter of the base material. The increased concentration of impurities in the center of the disk is due to the central portion of the disk cooling at a slower rate than the outer portion of the disk. Moreover, a metal flow, which is a flow of metal structure formed in the process of rolling or the like, is formed along the axis of the base material mass.
When the mass, which contains much of impurities around the central portion, is subjected to machining to manufacture the disk 80, much of impurities are present in a densely hatched portion X1 of FIG. 17 in the vicinity of the inner surface 83a of the mounting hole 83 from the bottom surface 84 to the end surface 81a of the protrusion 81. Besides, metal flows J are formed along the axis P1 of the disk 80.
For this reason, the disk 80 manufactured by machining is apt to fracture in the portion X1 which includes a lot of impurities along the metal flow lines J since a great stress acts especially on the end surface 81a of the protrusion 81 as compared with general mechanical parts. Accordingly, a disk 80 manufactured by machining has had a tendency to have a relatively shorter life span because of higher stresses applied to the end face, which in turn results in a shorter life span of a toroidal type continuously variable transmission.
In the manufacturing method described in the Jpn. Pat. Appln. Publication No. 9-126289, one kind of a die set is used for forging of a work for a disk till an almost final shape is conferred to the work and thereafter, grinding is applied to attain the disk 80. In the manufacturing method, therefore, a time length during which the work is in contact with the die set is long. Hence, the die set is apt to shorten its lifetime because of reduction in a surface hardness under influence of heat in forging.
In addition, since a structure of the die set is not one to support a work in the course of forging, the work is subject to deviate from the center of the die set to have an eccentricity, which causes dimensional precision to be deteriorated. Furthermore, since in the final stage of forging, the work occupies a full space of the die set, a part of the work corresponding to a corner of the die set is subject to underfill or burr, which have again caused shaping of the work into desired dimensions to be difficult.
What""s worse, since only one kind of die set is used, a need has arisen that an excessive load is imposed for forging a work in the process in order to mold the work into a desired shape. Hence, there has been a risk that a die set is fractured. In order to suppress a required time length for grinding which is performed after the forging, it is a necessity to decrease a grinding removal. In order to decrease the grinding removal, there is a further necessity to suppress a wear of the die set or the like. For this purpose, in the manufacturing method described in Jpn. Pat. Appln. Publication No. 9-126289, since one kind of die set is used and an excessive load is imposed on a die set in forging, a lifetime of the die set which is used in the forging has had a tendency to be shortened. Accordingly, a tendency to increase a production cost of a disk has arisen.
It is, accordingly, an object of the present invention to provide a toroidal type continuously variable transmission with a disk having a long lifetime and a method of manufacturing the disk for a toroidal type continuously variable transmission whereby not only can the disk having a long lifetime be molded with no shortening of a lifetime of die sets but increase in a production cost of the disk is suppressed.
The present invention, which has been made in order to achieve the object, is directed to a toroidal type continuously variable transmission comprising:
an input shaft rotated by a driving source;
an input disk supported on the input shaft;
an output disk supported on the input shaft and opposed to the input disk;
a power roller swingably provided between the input disk and the output disk and rotatably put in contact with both disks; and
a compression device having a cam disk supported on the input disk,
wherein at least one of the input disk and the output disk is provided with a protrusion projected along an axis thereof in the central portion and a mounting hole penetrating through the protrusion along the axis,
a portion including much of impurities of 30% or less of the outer diameter of the work around the central portion thereof, before manufacturing processes for the at least one disk, does not exist on a part of an inner surface of the mounting hole, which part extends a distance h from end surface of the protrusion and if a thickness of the disk in axial direction thereof is expressed H, the following a relationship is satisfied: h/Hxe2x89xa60.33.
In the toroidal type continuously variable transmission, the portion which includes much of impurities does not exist on a part of the inner surface of the mounting hole being extended toward an end surface of the protrusion to a position which satisfies the ratio of 0.33 or less. Hence, the toroidal type continuously variable transmission enjoys a long lifetime in use since the disk is prevented from being subjected to fracture at the end surface of the at least one disk.
It is desired that in the toroidal type continuously variable transmission, at least one of the input disk and the output disk is provided with: a protrusion projecting in the central portion along the axis thereof; and a traction surface which is put in contact with the power roller; and an end flow of a metal flow does not exist within the range of 15 to 60 degrees in an angle formed between a line segment V1, V2 between an end of a metal flow on the traction surface and a center of a curvature of the traction surface, and a line V which passes through the center of the curvature in parallel to the axis, respectively.
In the toroidal type continuously variable transmission, the traction surface which is put in contact with the power roller and a relatively large force is acted on does not have an end flow of a metal flow within the angular range of 15 to 60 degrees. Hence, the toroidal type continuously variable transmission is prevented from being fractured at the traction surface of the at least one disk and enjoys a long life time in use.
It is, besides, desired that at least one of the input disk and the output disk is provided with; a protrusion, which has an end surface, and which projects in the central portion thereof along the axis; a bottom surface located on the rear side of the end surface of the protrusion; and a traction surface which is put in contact with the power roller, and end flow of a metal flow on the bottom surface does not exist in the angular range of xc2x110 degrees of a line segment V3, that perform extensively between a center of a curvature of the traction surface and a contact point at which the power roller is put in contact with the traction surface at the maximum decrease in speed or the maximum increase in speed.
The toroidal type continuously variable transmission does not have end flow of a metal flow on the bottom surface located on the rear side of the end surface in the above described angular range. Hence, the toroidal type continuously variable transmission is prevented from being fractured at the bottom surface of at least one disk and enjoys a long lifetime in use.
The present invention is directed to a method of manufacturing a disk for a toroidal type continuously variable transmission, wherein the disk comprises: a protrusion projected in the central portion along the axis thereof; a skirt portion provided outside the periphery of the protrusion, and whose thickness is gradually thinner along a direction from the protrusion toward its outer edge; a mounting hole penetrating through the protrusion along the axis thereof; and a traction surface which is put in contact with a power roller,
characterized in that the method comprises of:
prepare a first cylindrical shaped material with metal flow existing on crosssectional surface thereof and extending along an axial direction thereof;
provide a first lower die comprising:
a first plane portion perpendicular to an axis (Q) of the first material;
a first circular recessed portion being from the first plane portion, having a diameter equal or larger than a diameter of the first material and being concentrical with the first material; and
provide a first upper die comprising:
a second plane portion perpendicular to an axis (Q) of the first material and having a diameter equal or larger than a diameter of the first material;
a second tapered recessed portion located outside of the second plane portion, the second tapered recessed portion decreasing in diameter in an upward direction and being concentrical with the first circular recessed portion of the first lower die and having taper angle (xcex8) equal to following equation:
xcex8=xcex4xc2x110 degrees,
wherein the angle xcex4 is formed between an end surface of the protrusion perpendicular to an axis of the disk and connecting line from xcex3 point to xcex2 point, the xcex3 point being edge of traction surface of the protrusion, xcex2 point on the traction surface being intersected to a horizontal line passed through a center (xcex1) of a curvature of the traction surface and parallel the axis of the disk;
upsetting the first material in the axial direction thereof with the first lower die and the first upper die so as to obtain a second material;
prepare a second lower die comprising:
a third plane portion perpendicular to an axis of the second material;
a first projecting portion being projected from a center of the third plane portion and being concentrical with the second material and;
a first outer portion located outside of the third plane portion, being concentrical with the second material;
prepare a second upper die comprising:
a fourth plane portion perpendicular to an axis of the second material and having a diameter equal the diameter of the second plane portion of the first upper die;
a third tapered recessed portion located outside of the fourth plane portion with same angle to the second tapered recessed portion of the first upper die;
a first inner die projected from a center of the fourth plane portion on concentrical with the second material and being formed in a conical shaped;
first forging the second material in the axial direction thereof with the second lower die and the second upper die so as to obtain a third material;
prepare a third lower die comprising:
a fifth plane portion perpendicular to an axis of the third material;
a second projecting portion being projected from a center of the fifth plane portion and being concentrical with the third material and;
a second outer portion located outside of the fifth plane portion, being concentrical with the third material and having a diameter for manufacturing a finished raw diameter of an outer peripheral surface of the disk;
prepare a third upper die comprising:
a fourth recessed portion for forming raw protrusion perpendicular to an axis of the third material;
a forming raw traction surface located outside of the fourth recessed portion for forming the traction surface of the concave arc shaped cross section and;
a second inner die projected concentrically with the third material and being diameter equal to first inner die;
second forging the third material in the axial direction thereof with the third lower die and the third upper die so as to obtain a fourth material, which the fourth material to finish the disk is obtained.
The method of manufacturing a disk for a toroidal type continuously variable transmission is that in the course in which a disk is molded from base material, portions corresponding to a protrusion, a mounting hole and a skirt portion are respectively molded using the first to third lower and upper dies in a separate manner. Hence, a time in which the work and each of the lower and upper dies stay in contact with each other is shortened and an influence of a work temperature on the lower and upper dies is lessened, which in turn entails a retained surface hardness of each of the lower and upper dies. Accordingly, not only is a chance of decreasing a lifetime of each die set smaller but increase in production cost thereof can be suppressed.
Besides, since the first to third lower and upper dies which are respectively used in the upsetting, the first forging and the second forging processes are separately provided, molding of the work in the respective processes can be performed with no troubles. Hence, flowing of a metal structure of the materials in each process can be effected in a smooth manner and a disk balanced in the flow of a metal structure or the like can be molded. Accordingly, a disk with a relatively long lifetime can be molded.
Besides, as described above, since the flowing of a metal structure of the disk in each of the processes can be effected in a smooth manner, pressures imposed on the lower and upper dies in the respective processes can be suppressed to a low level. Therefore, fracture of the lower and upper dies can be prevented from occurring. Accordingly, a lifetime of each lower and upper die is not shortened and at the same time, decrease in production cost is suppressed.
The first upper die which is used in the upsetting has a second plane portion, which is having a diameter equal or larger than diameter of the first material, and a second tapered recessed portion which is provided with satisfying the above described conditions. An inner profile of the second tapered recessed portion is in conformity with an outer profile of the protrusion of a disk when the second tapered recessed portion satisfies the above described conditions. Hence, a portion corresponding a protrusion of a disk can be molded on the second material by the upsetting process with certainty.
In the first lower die used in the upsetting, a first circular recessed portion which is formed in a withdrawn manner from a first plane portion retains the first material so that the axis of the material is perpendicular to the first plane portion. The center of the first circular recessed portion of the first lower die and the center of the second plane portion of the first upper die are in alignment with the axis of the material. Hence positional deviation such as an eccentricity of the material between the first lower die and the first upper die can be suppressed in upsetting the material. Accordingly, a disk with more of precision can be molded.
The second upper die which used in first forging is provided with the third tapered recessed portion with the same shape as the second tapered recessed portion of the first upper die. Hence, positional deviation such as eccentricity of the material is more suppressed and a disk with more of precision can be molded.
The first inner die has the outer diameter smaller than an inner diameter of a mounting hole. Hence, a portion including much of impurities of 30% or less of the outer diameter of the first material around the central portion thereof can be pushed out from the inner surface of the mounting hole or the like to be removed to nothing. Accordingly, a disk with a long lifetime can be molded.
The outer portion of the second lower die is formed as an annular ring enveloping the outer peripheral surface of the first material. Hence, positional deviation such as an eccentricity of the material is more suppressed and a disk with more of precision can be molded.
The third upper die used in second forging is provided with the forming raw traction surface whose inner profile is in conformity with the protrusion of the disk and the curved surface which is conformity with the traction surface. The second inner die is formed in the same shape as the first inner die. The outer portion of the third lower die is formed as an annular ring enveloping the outer periphery of the material. Hence, positional deviation such as an eccentricity of the material is more suppressed and a disk with more of precision can be molded.
It is desirable that in the upsetting, the first and second forging processes in which the protrusion, the mounting hole and the skirt portion are molded, the disk is molded while both ends of a base material mass is kept in contact with the first to the third lower and upper dies to be restrained by the dies.
The portion of a base material including most of the impurities and occurring in an area defined by a diameter that is 30% or less of the outer diameter of the base material mass. This portion is pushed out from a peripheral portion of the mounting hole, such as the inner surface thereof is mostly void of impurities and the invention can keep the value h/Hxe2x89xa60.33.
The disk may be manufactured by applying machining or the like after the upsetting, the first and second forging processes. In this case, not only can a disk with more of precision be manufactured but requirements for precision of the first to the third lower and upper dies when the dies are used for molding can be alleviated. Hence, even a die whose wear has been advanced can be kept in use and thereby, a production cost can be suppressed since a die cost is decreased.
It is desired that as a work for manufacturing the disk, a solid base material, which is formed in the shape of a round rod, and which has a flow of a metal structure (a metal flow) along an axial direction of the material is used. Besides, it is desired that when a length of the solid base material mass is L and a diameter thereof is d, L and d satisfy a relation of L/dxe2x89xa62.2.
In this case, when a disk is molded through the upsetting, the first and second forging processes, a metal flow is formed in an axial symmetrical relation with respect to the axis of the disk and the disk with a long lifetime can be molded.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.